High rate of seroeligibility among MYBPC3-associated hypertrophic cardiomyopathy patients for TN-201, an adeno-associated virus serotype 9 MYBPC3 gene therapy

Milind Desai^1*Daniele Massera²Heng Wang³Timothy C Wong⁴Omar Wever-Pinzon⁵Neal K Lakdawala⁶John Giudicessi⁷Theodore Abraham⁸Sherif Nagueh⁹Florian Rader¹⁰Ahmad Masri¹¹Emre Turer¹²Pfumo Mushonga¹³Elizabeth Butala Flores¹³William Harrison¹⁴Natalia Paterson¹⁴Gretchen Argast¹⁴

• ¹Cleveland Clinic, Cleveland, United States
• ²New York University, New York, United States
• ³DDC Clinic, Ohio, United States
• ⁴University of Pittsburgh, Pittsburgh, United States
• ⁵University of Miami, Coral Gables, United States
• ⁶Brigham and Women's Hospital, Boston, United States
• ⁷Mayo Clinic Minnesota, Rochester, United States
• ⁸University of California San Francisco, San Francisco, United States
• ⁹Houston Methodist Hospital, Houston, United States
• ¹⁰Cedars-Sinai Medical Center, Los Angeles, United States
• ¹¹Oregon Health & Science University, Portland, United States
• ¹²The University of Texas Southwestern Medical Center, Dallas, United States
• ¹³Bioagilatyx, North Carolina, United States
• ¹⁴Tenaya therapeutics, San Francisco, United States

Key words: Seroprevalence, AAV9, HCM Word count: 299 Abstract: Background The genetic etiology of hypertrophic cardiomyopathy (HCM) and the critical role of sarcomeric variants in its pathogenesis are well recognized.1 Among these, loss of function variants in myosin binding protein C gene (MYBPC3) are the most prevalent, resulting in protein insufficiency when compared to healthy controls.1 Preclinical studies have shown that recombinant adeno-associated virus serotype 9 (rAAV9) carrying the full-length MYBPC3 transgene can increase protein expression and improve cardiac function. However, pre-existing anti-AAV9 antibodies—neutralizing (NAb) and total (TAb)—may limit gene transfer efficacy and eligibility for gene therapy. We sought to evaluate the prevalence of anti-AAV9 antibodies in patients with MYBPC3-associated HCM to optimize patient selection for MyPEAK-1, an ongoing trial evaluating the safety, tolerability, and pharmacodynamics of TN-201, an AAV9:MYBPC3 gene therapy. Methods: This was a prospective, cross-sectional study of 100 adults (aged 18–65 years) with symptomatic MYBPC3-associated HCM (NYHA II–IV). Blood samples were analyzed for anti-AAV9 NAb (transduction inhibition assay) and TAb (electrochemiluminescence assay). Titers ≥1:10 were considered positive. Associations between antibody levels and demographic and clinical characteristics were explored using statistical tests. Results: Pre-existing anti-AAV9 NAb were undetectable in 50% of patients. Among those with detectable titers (range: 1:10–1:720), only 16% exceeded 1:40. TAb were undetectable in 53%; titers ranged from 1:10 to 1:65,600. A strong correlation was observed between NAb and TAb titers (r=0.671, p<0.001). Serostatus was not significantly associated with age, sex, NYHA class, or ethnicity (all p>0.05). Conclusions: Pre-existing immunity to AAV9 was absent or low in most MYBPC3-associated HCM patients, with only a small proportion exceeding standard NAb thresholds for AAV gene therapy trials. These findings support the feasibility of a clinical trial of TN-201, an AAV9-based MYBPC3 gene replacement therapy, in this population. Given the concordance between NAb and TAb assays, either may be suitable for screening.